Method of operating relay station in wireless communication system

ABSTRACT

A method of operating a relay station in a wireless communication system is provided. The method includes operating in a first mode comprising a first sub-mode and a second sub-mode, in the first sub-mode a first downlink and a first uplink between a base station and the relay station being simultaneously activated, in the second sub-mode a second downlink and a second uplink between the relay station and a mobile station being simultaneously activated, and operating in a second mode comprising a third sub-mode and a fourth sub-mode, in the third sub-mode the first downlink and the second uplink being simultaneously activated, in the fourth sub-mode the first uplink and the second downlink being simultaneously activated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/166,315 filed on Jan. 28, 2014, now allowed; which is a continuationof U.S. application Ser. No. 12/588,725 filed on Oct. 26, 2009, nowissued as U.S. Pat. No. 8,675,542; which claims priority to U.S.Provisional Application No. 61/117,957 filed on Nov. 26, 2008 and U.S.Provisional Application No. 61/108,857 filed on Oct. 27, 2008, andKorean Patent Application No. 10-2009-0064415 filed on Jul. 15, 2009,all of which are incorporated by reference in their entirety herein.

BACKGROUND

1. Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a method of operating a relay station in a wirelesscommunication system.

2. Related Art

Wireless communication systems are widely spread all over the world toprovide various types of communication services such as voice or data.In general, the wireless communication system is a multiple accesssystem capable of supporting communication with multi-users by sharingavailable radio resources. Examples of the radio resource include atime, a frequency, a code, transmit power, etc. Examples of the multipleaccess system include a time division multiple access (TDMA) system, acode division multiple access (CDMA) system, a frequency divisionmultiple access (FDMA) system, an orthogonal frequency division multipleaccess (OFDMA) system, a single carrier frequency division multipleaccess (SC-FDMA) system, etc. The radio resource is a time in the TDMAsystem, a frequency in the FDMA system, a code in the CDMA system, and asubcarrier and a time in the OFDMA system. A wireless communicationsystem is a system supporting bidirectional communication. Thebidirectional communication can be performed by using a time divisionduplex (TDD) mode, a frequency division duplex (FDD) mode, ahalf-frequency division duplex (H-FDD) mode, etc. The TDD mode uses atime resource to identify uplink transmission and downlink transmission.The FDD mode uses a frequency resource to identify uplink transmissionand downlink transmission. The H-FDD mode uses a combination of a timeresource and a frequency resource to identify uplink transmission anddownlink transmission.

The wireless communication system includes a base station (BS) providinga service to a specific region (i.e., a cell). According to acharacteristic of a wireless transmission technology, changes in awireless environment have an effect on quality of signal transmitted. Inparticular, due to various factors in a surrounding environment, such asscatters, movement of a mobile station (MS), etc., a wireless channelchanges over time. In addition, there is a restriction in terms ofdistance since reception power is rapidly decreased in proportion to adistance between wireless communication entities. Therefore, in general,the MS can communicate with the BS when the MS is located within thecoverage of the BS. As such, due to several factors such as thescatters, a movement speed of the MS, a distance between transmissionand reception, etc., a maximum transfer rate, a throughput of anintra-cell user, and a throughput of a whole cell are decreased betweenthe BS and the MS. For example, when the MS is located in a cellboundary or when an obstacle such as a building exists between the MSand the BS, communication quality between the MS and the BS may not besatisfactory.

As an effort to overcome the aforementioned problem, several techniquesare introduced to compensate for deterioration of signals transmittedbetween the BS and the MS, thereby obtaining a maximum transfer rate,throughput improvement, coverage expansion, etc. For this purpose, awireless communication system may employ a relay station (RS). The RScan expand the coverage of the BS, and can improve a cell throughput.

According to functions of the RS, the RS can be classified into severaltypes as follows.

TABLE 1 L3 Pico/Femto function L1 Relay L2 Relay Relay Cell RF functionX X X X Coder/Decoder and CRC — X X X HARQ — X X X Multiplex &Demultiplex — X X X of MAC SDU Priority (Qos) handling — X X XScheduling — X X X Outer ARQ — (X) X X (Re)-Segmentation and — (X) X Xconcatenation Header — — — X compression (ROHC) Reordering of lower — —— X layer SDUs In-sequence delivery of — — — upper layer PDUs Duplicatedetection of — — — X lower layer SDUs Ciphering — — — X Systeminformation — — X X broadcast RRC Connection set-up — — X X andmaintenance Radio Bearers set-up — — — X and maintenance Mobilityfunction — — X MBMS services control — — — X Paging — — — X QoSmanagement — — (X) X UE measurement — — (X) X reporting and control thereporting NAS signalling handling — — — X

Although the RS is classified into an L1 relay, an L2 relay, and an L3relay in Table 1, this is for exemplary purposes only. The aboveclassification is achieved according to a broad characteristic of theL1, L2, and L3 relays, and the terminology thereof is not limitedthereto. By reference, Table 1 also provides a function of a femto cellor a pico cell. It is assumed that the femto cell or the pico cellsupports all functions exemplified in Table 1. The L1 relay is an RShaving an amplify and forward (AF) function as well as some additionalfunctions. The L1 relay amplifies a signal received from a BS or an MSand delivers the amplified signal to the MS or the BS. The L2 relay isan RS having a decoding and forward (DF) function as well as ascheduling function. The L2 relay restores information by performingdemodulation and decoding on a signal received from the BS or the MS,generates a signal by performing coding and modulation, and thendelivers the generated signal to the MS or the BS. The L3 relay is an RShaving a configuration similar to one cell. The L3 relay has thefunctions of the L2 relay and supports call access, release, andmobility functions.

The RS can transmit or receive data by using a radio resource. The radioresource that can be used by the RS includes a time resource, afrequency resource, a spatial resource, etc. The time resource isexpressed by a subframe, a symbol, a slot, etc. The frequency resourceis expressed by a subcarrier, a resource block, a component carrier,etc. The spatial resource is expressed by spatial multiplexing, anantenna, etc. Such a radio resource may be used in a dedicated or sharedmanner between the BS and the RS or between the RS and the MS.

The RS is a recently introduced concept, and has to support an MSdevised without consideration of the RS. For example, although the RS isnot considered in the long term evolution (LTE) standard, the RS has tosupport not only an MS conforming to the LTE-advance standard but alsoan MS conforming to the LTE standard.

SUMMARY

The present invention provides a method of effectively transmitting andreceiving a signal by using a relay station (RS). The present inventionalso provides a method of operating an RS that can support a mobilestation (MS) devised without consideration of the RS.

According to an aspect of the present invention, a method of operating arelay station in a wireless communication system is provided. The methodincludes operating in a first mode comprising a first sub-mode and asecond sub-mode, in the first sub-mode a first downlink and a firstuplink between a base station and the relay station being simultaneouslyactivated, in the second sub-mode a second downlink and a second uplinkbetween the relay station and a mobile station being simultaneouslyactivated, and operating in a second mode comprising a third sub-modeand a fourth sub-mode, in the third sub-mode the first downlink and thesecond uplink being simultaneously activated, in the fourth sub-mode thefirst uplink and the second downlink being simultaneously activated.

According to another aspect of the present invention, a method ofoperating a relay station in a wireless communication system isprovided. The method includes communicating with a base station througha backhaul link between the base station and the relay station, andcommunicating with a mobile station connected to the relay stationthrough an access link between the relay station and the mobile station.The backhaul link and the access link are activated according to aspecific rule.

According to yet another aspect of the present invention, a relaystation is provided. The relay station includes a radio frequency (RF)unit for transmitting and receiving a radio signal, and a processorcoupled to the RF unit. The processor operates in a first modecomprising a first sub-mode and a second sub-mode. In the first sub-modea first downlink and a first uplink between a base station and the relaystation is simultaneously activated. In the second sub-mode a seconddownlink and a second uplink between the relay station and a mobilestation is simultaneously activated. The processor also operates in asecond mode comprising a third sub-mode and a fourth sub-mode, in thethird sub-mode the first downlink and the second uplink issimultaneously activated, and in the fourth sub-mode the first uplinkand the second downlink is simultaneously activated.

According to the present invention, there is provided a method ofoperating a relay station (RS) that can support not only a mobilestation (MS) devised in consideration of the RS but also an MS devisedwithout consideration of the RS. In addition, there is also provided asubframe configuration satisfying backward compatibility with respect tohybrid automatic repeat request (HARQ) defined by the long termevolution (LTE) standard.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a wireless communication system employing arelay station (RS).

FIG. 2 shows a structure of a frequency division duplex (FDD) radioframe of a 3rd generation partnership project (3GPP) long term evolution(LTE) system.

FIG. 3 shows a structure of a time division duplex (TDD) radio frame ofa 3GPP LTE system.

FIG. 4 shows an example of an operation of a time division multiplexing(TDM) RS.

FIG. 5 shows an operation mode that can be used by an RS.

FIG. 6 is a flowchart showing a method of operating an RS in a wirelesscommunication system employing the RS according to an embodiment of thepresent invention.

FIG. 7 shows an operation of an RS according to an embodiment of thepresent invention.

FIG. 8 to FIG. 11 show operations of an RS according to an embodiment ofthe present invention.

FIG. 12 shows a subframe configuration of an RS according to anembodiment of the present invention.

FIG. 13 shows a subframe configuration of an RS according to anotherembodiment of the present invention.

FIG. 14 and FIG. 15 show link usage efficiency depending on the numberof hybrid automatic repeat request (HARQ) processes when a subframe isconfigured according to an embodiment of the present invention.

FIG. 16 is a block diagram showing an RS according to an embodiment ofthe present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technique described below can be used in various wireless accesstechnologies such as code division multiple access (CDMA), frequencydivision multiple access (FDMA), time division multiple access (TDMA),orthogonal frequency division multiple access (OFDMA), single carrierfrequency division multiple access (SC-FDMA), etc. The CDMA may beimplemented with a radio technology such as universal terrestrial radioaccess (UTRA) or CDMA2000. The TDMA may be implemented with a radiotechnology such as global system for mobile communications (GSM)/generalpacket radio service (GPRS)/enhanced data rates for GSM evolution(EDGE). The OFDMA may be implemented with a radio technology such asinstitute of electrical and electronics engineers (IEEE) 802.11 (Wi-Fi),IEEE 802.16 (WiMAX), IEEE 802-20, evolved-UTRA (E-UTRA) etc. The UTRA isa part of a universal mobile telecommunication system (UMTS). 3rdgeneration partnership project (3GPP) long term evolution (LTE) is apart of an evolved-UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE employsthe OFDMA in a downlink and employs the SC-FDMA in an uplink.

For clarity of explanation, the following description will focus on the3GPP LTE. However, the technical features of the present invention arenot limited thereto.

FIG. 1 is a diagram showing a wireless communication system employing arelay station. The wireless communication system can be widely deployedto provide a variety of communication services, such as voices, packetdata, etc.

Referring to FIG. 1, the wireless communication system includes mobilestations (MSs) 10, 11, 12, and 13, a base station (BS) 20, and relaystations (RSs) 30 and 31. Each of the MSs 10, 11, 12, and 13 may befixed or mobile, and may be referred to as another terminology, such asa user equipment (UE), a user terminal (UT), a subscriber station (SS),a wireless device, etc. The BS 20 is generally a fixed station thatcommunicates with the MSs 10, 11, 12, and 13 and may be referred to asanother terminology, such as a node-B (NB), a base transceiver system(BTS), an access point, etc. One or more cells may exist in the coverageof one BS 20. The RSs 30 and 31 are provided for coverage extension ordata transfer rate improvement resulted from a diversity effect, and arelocated between the MS and the BS. The RS may be referred to as anotherterminology, such as a repeater, a relay, a relay node (RN), etc. Thatis, the MSs 10 and 11 located inside the coverage of the BS 20 candirectly communicate with the BS 20, and the MSs 12 and 13 locatedoutside the coverage of the BS 20 communicate with the BS 20 via the RSs30 and 31. Alternatively, for the data transfer rate improvementresulted from the diversity effect, even the MSs 10 and 11 locatedinside the coverage of the BS 20 may communicate with the BS 20 via theRSs 30 and 31.

A downlink (DL) implies communication from the BS 20 to the MS 10, fromthe BS 20 to the RS 30, or from the RS 30 to the MS 10. An uplink (UL)implies communication from the MS 10 to the BS 20, from the MS 10 to theRS 30, or from the RS 30 to the BS 20. The UL and the DL between the BSand the RS are backhaul links. The UL and the DL between the BS and theMS or between the RS and the MS are access links. Hereinafter, forconvenience of explanation, the UL between the BS and the RS is referredto as a 1st UL, the DL between the BS and the RS is referred to as a 1stDL, the UL between the RS and the MS is referred to as a 2nd UL, and theDL between the RS and the MS is referred to as a 2nd DL. The 1st DL andthe 1st UL between the BS and the RS may operate in a frequency divisionduplex (FDD) mode or a time division duplex (TDD) mode. The 2nd DL andthe 2nd UL between the RS and the MS may also operate in the FDD mode orthe TDD mode.

FIG. 2 shows a structure of an FDD radio frame of a 3GPP LTE system. Thesection 4.1 of 3GPP TS 36.211 “Technical Specification; EvolvedUniversal Terrestrial Radio Access (E-UTRA); Physical Channels andModulation (Release 8)” may be incorporated herein by reference. When inthe FDD mode, DL transmission and UL transmission are divided in afrequency domain.

Referring to FIG. 2, the radio frame consists of 10 subframes, and onesubframe consists of two slots. For example, one subframe may have alength of 1 millisecond (ms), and one slot may have a length of 0.5 ms.The slot may consist of 7 symbols in case of a normal cyclic prefix(CP), and may consist of 6 symbols in case of an extended CP.

A primary-synchronization channel (PSCH) and a secondary-synchronizationchannel (SSCH) may be allocated to some symbols of a 1st subframe andsome symbols of a 6th subframe among DL subframes. A broadcast channelmay also be allocated to some symbols of the 1st subframe and somesymbols of the 6th subframe. When power is resumed in a power-off stateor when an MS newly enters a cell, the MS performs an initial cellsearch operation for synchronization with a BS. For this, the MS may besynchronized with the BS by receiving the PSCH and the SSCH from the BS,and may obtain information such as a cell identifier (ID) or the like.Thereafter, the MS may receive the broadcast channel from the BS toobtain intra-cell broadcast information. Meanwhile, the MS may receive aDL reference signal (RS) in the initial cell search operation toevaluate a DL channel condition.

The radio frame structure of FIG. 2 is for exemplary purposes only, andthus the number of subframes included in the radio frame or the numberof slots included in the subframe may change variously.

FIG. 3 shows a structure of a TDD radio frame of a 3GPP LTE system. Thesection 4.2 of 3GPP TS 36.211 “Technical Specification; EvolvedUniversal Terrestrial Radio Access (E-UTRA); Physical Channels andModulation (Release 8) may be incorporated herein by reference.

Referring to FIG. 3, a radio frame consists of two half-frames. Thehalf-frame consists of five subframes.

A UL and a DL are identified in a subframe unit. A UL subframe and a DLsubframe are separated by a switching point. The switching point is aregion for separating the UL and the DL between the UL subframe and theDL subframe. The radio frame has at least one switching point. Theswitching point includes a downlink pilot time slot (DwPTS), a guardperiod (GP), and an uplink pilot time slot (UpPTS). The DwPTS is usedfor initial cell search, synchronization, or channel estimation. TheUpPTS is used for channel estimation in the BS and for UL transmissionsynchronization of the MS. The GP is a guarding duration for removinginterference generated in the UL due to a multi-path delay of a DLsignal between the UL and the DL.

Table 2 shows a structure of a radio frame that can be configuredaccording to an arrangement of a UL subframe and a DL subframe in theLTE TDD system.

TABLE 2 Uplink- Downlink- downlink to-Uplink configu- Switch-pointSubframe number ration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U UD S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 msD S U U U D D D D D 4 10 ms D S U U D D D D D D 5 10 ms D S U D D D D DD D 6 5 ms D S U U U D S U U D

‘D’ denotes a DL subframe. ‘U’ denotes a UL subframe. ‘S’ denotes aspecial subframe. The special subframe indicates a switching point, thatis, DwPTS+GP+UpPTS. In configurations 0 to 2 and a configuration 6, theUL and the DL are switched with a switching point period of 5 ms. Inconfigurations 3 to 5, the DL and the UL are switched with a switchingpoint period of 10 ms.

Table 3 shows a method of configuring the DwPTS, the GP, and the UpPTSconsidered in the LTE system. Ts denotes a sampling time, and iscalculated by 1/(15000*2048) (sec).

TABLE 3 Normal cyclic prefix in downlink Extended cyclic prefix indownlink UpPTS UpPTS Normal Extended Normal Extended Special subframecyclic prefix cyclic prefix cyclic prefix cyclic prefix configurationDwPTS in uplink in uplink DwPTS in uplink in uplink 0  6592 · T_(s) 2192· T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 1 19760 ·T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 · T_(s) 25600· T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 · T_(s) 5  6592· T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 · T_(s) 23040 ·T_(s) 7 21952 · T_(s) — — — 8 24144 · T_(s) — — —

Regarding a special subframe, 9 combinations are possible in case of anormal cyclic prefix, and 7 combinations are possible in case of anextended cyclic prefix.

FIG. 4 shows an example of an operation of a time division multiplexing(TDM) RS. In the following description, an MS is connected to the RS,and may be either an MS conforming to the LTE standard (hereinafter, LTEMS) or an MS conforming to the LTE-advance standard (hereinafter, LTE-AMS). It is assumed that 1st DL transmission and 2nd DL transmission usethe same frequency band, and 1st UL transmission and 2nd UL transmissionuse the same frequency band. It is also assumed that DL transmission andUL transmission use different frequency bands.

Referring to FIG. 4, in a subframe #0, if the RS receives a signal fromthe BS through the 1st DL, the RS cannot transmit a signal to the MSthrough the 2nd DL. In a subframe #1, if the RS transmits a signal tothe MS through the 2nd DL, the RS cannot receive a signal from the BSthrough the 1st DL. In a subframe #5, if the RS receives a signal fromthe MS through the 2nd UL, and the RS cannot transmit a signal to the BSthrough the 1st UL. In a subframe #6, if the RS transmits a signal tothe BS through the 1st UL, the RS cannot receive a signal from the MSthrough the 2nd UL. As such, the RS cannot simultaneously transmit andreceive signals by using the same frequency band.

FIG. 5 shows an operation mode that can be used by an RS.

Referring to FIG. 5a , when a 1st DL and a 1st UL between a BS and an RSare activated, a 2nd DL and a 2nd UL between the RS and an MS areinactivated, and when the 2nd DL and the 2nd UL between the RS and theMS are activated, the 1st DL and the 1st UL between the BS and the RSare inactivated. This will be hereinafter referred to as a first mode.

Referring to FIG. 5b , when a 1st DL between a BS and an RS and a 2nd ULbetween the RS and an MS are activated, a 2nd DL between the RS and theMS and a 1st UL between the BS and the RS are inactivated, and when the1st UL between the BS and the RS and the 2nd DL between the RS and theMS are activated, the 2nd UL between the RS and the MS and the 1st DLbetween the BS and the RS are inactivated. This will be hereafterreferred to as a second mode.

As shown in FIG. 4 and FIG. 5, when the 1st DL is activated, the 2nd DLis inactivated. Therefore, an MS connected to the RS cannot receive a DLsignal in a corresponding subframe. In this case, among MSs connected tothe RS, there may exist an MS not knowing a fact that a DL signal cannotbe received in a corresponding subframe. An example thereof is aconventional MS (e.g., LTE MS) designed without consideration of the RS.Such an MS may attempt to receive data in a corresponding frame and mayperform channel quality measurement. Wrong channel quality measurementmay produce an erroneous operation of the MS, resulting in generation ofincorrect channel quality information. In addition thereto, a cellreconfiguration process may be performed, or a call may be completelyterminated. Therefore, there is a need for a method capable of solvingsuch a problem.

It is assumed that an MS enters a cell of the RS. In general, the MS isconnected to the cell of the RS by performing a cell switching processor the like. Due to limited capability of the RS, there is a case whereDL and/or UL transmissions cannot be achieved in a specific framebetween the RS and the MS. In this case, an MS designed in considerationof the RS may understand an operation of the RS and thus recognize aspecific subframe in which no transmission is performed, and thenperform a predetermined procedure. However, the conventional MS designedwithout consideration of the RS cannot recognize the specific subframein which no transmission is performed. Hereinafter, signaling of the RSfor the conventional MS designed without consideration of the RS will bedescribed.

FIG. 6 is a flowchart showing a method of operating an RS in a wirelesscommunication system employing the RS according to an embodiment of thepresent invention. Although signaling between the RS and an MS isexemplified herein for convenience of explanation, the same can also beequally applied between a BS and the RS.

Referring to FIG. 6, the MS is connected to a cell of the RS (stepS100). Herein, the MS may be a conventional MS designed withoutconsideration of the RS. For example, the MS may be an LTE MS. The MSmay be subjected to cell modification before being connected to the RS.In this case, it is assumed that, if a 1st DL is activated in a specificsubframe, a 2nd DL is inactivated, and if a 1st UL is activated in aspecific subframe, a 2nd UL is inactivated.

The RS performs subframe configuration of the RS (step S110), andtransmits subframe configuration information to the MS by signaling(step S120). For example, the subframe configuration information isexpressed by the table blow.

TABLE 4RelaySubframeConfiguration::=SEQUENCE(SIZE(1..maxRelayAllocations))OFSEQUENCE{ radioframeAllocationPeriod ENUMERATED{n1,n2,n4,n8,n16,n32},radioframeAllocationOffset INTEGER{0..7), subframeAllocationINTEGER{1..7)

As such, the RS may determine a radio frame allocation period (i.e.,radioframeAllocationPeriod), a radio frame allocation offset (i.e.,radioframeAllocationOffeset), a subframe allocation (i.e.,subframeAllocation) etc., and may report information thereon to the MS.In this case, the RS may perform signaling to the MS through a physicallayer or a higher layer. In addition, the RS may report the subframeconfiguration information to the MS by expressing the subframeconfiguration information in a bitmap format.

In addition thereto, the RS may determine to activate or inactivate the2nd DL and/or the 2nd UL in the specific subframe, and may reportinformation thereon to the MS. The RS may determine to activate orinactivate the 1st DL and/or the 1st UL in the specific subframe, andmay report information thereon to the MS. The specific subframe may bean odd-numbered subframe or an even-numbered subframe.

The RS may consider several aspects to configure the specific subframe.For example, the RS has to receive a synchronization channel (SCH)and/or a broadcast channel (BCH) from the BS. Therefore, it may bedetermined that the 2nd DL is inactivated in a specific subframe inwhich the SCH and/or the BCH are received. The specific subframe inwhich the SCH and/or the BCH are received may be a subframe #0 and/or asubframe #5. More specifically, when conforming to the LTE standard, theSCH is located in some symbols of the subframe #0 and the subframe #5and a physical broadcast channel (PBCH) is located in some symbols ofthe subframe #0. A dynamic broadcast channel (D-BCH) transmitted in aformat of a system information block (SIB) may be located in thesubframe #0 and the subframe #5, or may be located in any one of thesubframe #0 and the subframe #5 of an even-numbered radio frame.However, such locations of the SCH and the BCH are exemplary purposesonly, and thus may change depending on a communication system.

Accordingly, an error caused by wrong channel quality measurement can beprevented when the RS cannot transmit a signal to the MS while receivinga signal from the BS by using the same frequency band. In addition,hybrid automatic repeat request (HARQ) defined by the LTE standard andHARQ defined by the LTE-A standard can normally operate in an error-freemanner without having a significant change. That is, backwardcompatibility can be ensured.

Meanwhile, due to limited transmission/reception capability of the RS,the RS suffers significant restriction on link configuration. Ingeneral, the RS cannot simultaneously receive and transmit data over thesame frequency. Accordingly, a situation may occur in which data cannotbe transmitted in a specific subframe. A characteristic of the RS has aneffect on an HARQ operation. Therefore, the specific subframe can bedefined as a blank subframe. To overcome a problem caused by the limitedcapability of the RS, it is proposed to introduce an RS capable ofsupporting all operations or only some combinations of the operationsdescribed in FIG. 7 to FIG. 11.

FIG. 7 shows an operation of an RS according to an embodiment of thepresent invention. An arrow direction indicates a transmissiondirection. A solid line indicates data transmission. A dotted lineindicates control signal transmission. For example, a channel fortransmitting data is a shared channel (SCH), and a channel fortransmitting a control signal is a control channel (CCH).

Referring to FIG. 7a , when a 1st DL and a 1st UL between a BS and an RSare activated, a 2nd DL and a 2nd UL between the RS and an MS areinactivated. Referring to FIG. 7b , when a 2nd DL and a 2nd UL betweenan RS and an MS are activated between, a 1st DL and a 1st UL between aBS and the RS are inactivated. As such, a link between the BS and the RSand a link between the MS and the RS can be alternately activated. Forconvenience of explanation, a method of FIG. 7a will be referred to as afirst sub-mode, and a method of FIG. 7b will be referred to as a secondsub-mode. Considering that an LTE system uses an OFDMA scheme in DLtransmission and uses an SC-FDMA scheme in UL transmission, it ispreferable that the first sub-mode and the second sub-mode arealternately operated according to a condition of the RS. When the firstsub-mode and the second sub-mode are alternately operated, such anoperation mode is referred to as a first mode.

FIG. 8 to FIG. 11 show operations of an RS according to an embodiment ofthe present invention. An arrow direction indicates a transmissiondirection. A solid line indicates a channel for transmitting data. Adotted line indicates a channel for transmitting a control signal. Forexample, the channel for transmitting data is a shared channel (SCH),and the channel for transmitting a control signal is a control channel(CCH). The RS may be an FDD-type RS in which DL transmission and ULtransmission use different frequency bands. In addition, when the RSsupports an LTE or LET-A system, the RS may be an RS capable ofsimultaneously demodulating signals modulated using OFDMA and SC-FDMA.As a result, a time delay is minimized, and a degree of freedomincreases in system management. An RS based on the embodiment of thepresent invention supports an operation of FIG. 7, and may support alloperations or some combinations of the operations of FIG. 8 to FIG. 11.Accordingly, the RS based on the embodiment of the present invention candetermine an RS link configuration differently depending on a channelcondition or a system condition.

Referring to FIG. 8, when a 1st DL between a BS and an RS is activated,a 2nd DL between the RS and an MS is inactivated. In this case,according to the channel condition or the system condition, a 1st ULbetween the BS and the RS and a 2nd UL between the RS and the MS can beselectively activated.

Referring to FIG. 9, when a 2nd DL between an RS and an MS is activated,a 1st DL between a BS and the RS is inactivated. In this case, accordingto the channel condition or the system condition, a 2nd UL between theRS and the MS or a 1st UL between the BS and the RS can be selectiveactivated.

Referring to FIG. 10, when a 1st UL between a BS and an RS is activated,a 2nd UL between the RS and an MS is inactivated. In this case,according to the channel condition or the system condition, a 1st DLbetween the BS and the RS or a 2nd DL between the RS and the MS can beselectively activated.

Referring to FIG. 11, when a 2nd UL between an RS and an MS isactivated, a 1st UL between a BS and the RS is inactivated. In thiscase, according to the channel condition or the system condition, a 1stDL between the BS and the RS or a 2nd DL between the BS and the RS canbe selectively activated.

The method exemplified in FIG. 8 to FIG. 11 selects two links from threepossible links according to a condition. Although some parts of themethod of FIG. 8 to FIG. 11 are identical to those of the method of FIG.7, the identical parts are separately described herein for ideal modeidentification and for convenience of explanation.

To distinguish from the example of FIG. 7, a case where the 1st DLbetween the BS and the RS and the 2nd UL between the RS and the MS aresimultaneously activated is referred to as a third sub-mode. Inaddition, a case where the 1st UL between the BS and the RS and the 2ndDL between the RS and the MS are simultaneously activated is referred toas a fourth sub-mode. It is preferable that the third sub-mode and thefourth sub-mode are alternately operated according to a condition of theRS. As such, when the third sub-mode and the fourth sub-mode arealternately operated, such an operation mode is referred to as a secondmode.

The aforementioned operation mode of the RS can also extensively applyto HARQ. In this case, it can be assumed that the BS and the RS haveseparate scheduling functions, and the HARQ is performed between the RSand the MS in an independent manner to some extent. According to the LTEstandard, the HARQ has a period of 8 subframes. That is, a differencefrom an initial transmission time to a retransmission time is 8subframes. Since the HARQ is synchronous HARQ, this value is a fixedvalue. Such a restriction also directly applies to a UL between the BSand the RS.

FIG. 12 shows a subframe configuration of an RS according to anembodiment of the present invention. An MS may be an LTE-A MS (i.e.,MS 1) or an LTE MS (i.e., MS 2). The MS may be connected to the RS or aBS. It is assumed that the LTE MS can operate by being connected to theRS. In this case, a subframe index between the BS and the RS and asubframe index between the RS and the MS may be indexed in an identicalor different manner. It is exemplified in the present invention that thesubframe indices are indexed in an identical manner. If the subframeindex of the BS is indexed differently from the subframe index of theRS, the BS and the RS can share an index difference.

Referring to FIG. 12, in a subframe #0, a 1st UL and a 1st DL betweenthe BS and the RS are activated. In this case, the RS can receive SCHinformation and/or BCH information from the BS through the 1st DL, andcan transmit a signal to the BS through the 1st UL. Due to limitedcapability of the RS, in the subframe #0, a 2nd UL and a 2nd DL betweenthe RS and the MS are inactivated. Upon receiving the SCH information inthe subframe #0, the RS is synchronized with the BS. Upon receiving theBCH information, the RS prepares to transmit the BCH information to anMS connected to the RS.

Next, in a subframe #1, the 2nd UL and the 2nd DL between the RS and theMS are activated. In this case, the RS can transmit the BCH informationreceived from the BS in the subframe #0 to the MS through the 2nd DL,and can receive a signal from the MS through the 2nd UL. In the subframe#1, the RS can transmit the SCH information to the MS. The SCHinformation transmitted by the RS to the MS may be SCH informationgenerated by the RS itself.

Next, in a subframe #5, the 1st DL between the BS and the RS and the 2ndUL between the RS and the MS are activated. There is a case where the BSmust transmit specific control information to the RS in a specificsubframe. For example, in the subframe #5, the BS transmits SCHinformation and D-BCH information to the RS. Therefore, the 1st DLbetween the BS and the RS is activated, and the 2nd DL between the BSand the RS is inactivated. In this case, the 1st UL between the BS andthe RS or the 2nd UL between the RS and the MS can be selectivelyactivated. However, the 2nd UL between the RS and the MS has to beactivated so that synchronous HARQ is performed for data transmissionbetween the RS and the MS

The 1st DL activated in the subframe #5 between the BS and the RS maytransmit only control information or may transmit both the controlinformation and data. When the control information and the data aretransmitted, even if a UL scheduling grant is delivered, the data cannotbe transmitted through the 1st UL in a subframe #9. Therefore, it isassumed that the 1st DL activated in the subframe #5 between the BS andthe RS transmits only the control information. To avoid such arestriction, an HARQ process between the BS and the RS may be newlydesigned. For example, such a problem can be solved if data istransmitted after 3 or 5 subframes elapse from a time when the ULscheduling grant is received and if acknowledgment(ACK)/Non-acknowledgement (NACK) is received after 8 subframes elapse.That is, the problem can be solved if a subframe capable of transmittingdata is configured to an even-numbered subframe. In this case, theeven-numbered subframe is for exemplary purposes only, and thus thesubframe may also be configured to an odd-numbered subframe, a subframeindexed with a multiple of k, a subframe group determined by apre-defined pattern, etc. Information on the pre-defined pattern can beshared by signaling between the BS and the RS.

Next, in a subframe #6, the 2nd DL between the RS and the MS and the 1stUL between the BS and the RS are activated. In the subframe #6, the RStransmits SCH information and/or BCH information to the MS. Therefore,the 2nd DL between the RS and the MS is activated, and the 1st DLbetween the BS and the RS is inactivated. In this case, the 1st ULbetween the BS and the RS or the 2nd UL between the RS and the MS can beselectively activated. However, the 1st UL between the BS and the RS ispreferably activated so that synchronous HARQ is performed for datatransmission between the BS and the RS.

As such, a link between the BS and the RS and a link between the RS andthe MS may be alternately activated according to a specific rule. Forexample, the link between the BS and the RS may be activated in anodd-numbered subframe, and the link between the RS and the MS may beactivated in an even-numbered subframe. The link between the BS and theRS may be activated in the even-numbered subframe, and the link betweenthe RS and the MS may be activated in the odd-numbered subframe.Alternatively, the link between the RS and the MS may be activated in asubframe indexed with a multiple of k. Alternatively, the link betweenthe RS and the MS may be activated in a subframe corresponding to apre-defined pattern. Accordingly, HARQ for data transmission between theRS and the MS can be performed using an activated subframe. For example,it is assumed that the link between the RS and the MS is activated in anodd-numbered subframe. When the RS transmits a UL scheduling grant tothe MS through the 2nd DL in the subframe #1, the MS transmits data tothe RS through the 2nd UL (e.g., PUSCH channel) in the subframe #5, thatis, after four subframes elapse. In addition, in the subframe #9, thatis, after four subframes elapse from the subframe #5, the RS transmitsACK/NACK to the MS through the 2nd DL. When data retransmission isrequired, the MS transmits data to the RS through the 2nd UL in asubframe #3 of a next frame, that is, after four subframes elapse fromthe subframe #9. In a subframe next to the subframe in which the 2nd DLor the 2nd UL between the RS and the MS is activated, the 1st DL or the1st UL between the BS and the RS can be activated.

FIG. 13 shows a subframe configuration of an RS according to anotherembodiment of the present invention. In this case, a subframe indexbetween a BS and the RS and a subframe index between the RS and an MSmay be indexed in an identical or different manner. It is exemplified inthe present invention that the subframe indices are indexed in anidentical manner. If the subframe index of the BS is indexed differentlyfrom the subframe index of the RS, the BS and the RS can share an indexdifference.

Referring to FIG. 13, in a subframe #0, a 1st UL and a 1st DL betweenthe BS and the RS are activated. In this case, the RS can receive SCHinformation and/or BCH information from the BS through the 1st DL, andcan transmit a signal to the BS through the 1st UL. Due to limitedcapability of the RS, in the subframe #0, a 2nd UL and a 2nd DL betweenthe RS and the MS are inactivated. Upon receiving the SCH information inthe subframe #0, the RS is synchronized with the BS. Upon receiving theBCH information, the RS prepares to transmit the BCH information to anMS connected to the RS.

Next, in a subframe #1, the 2nd UL and the 2nd DL between the RS and theMS are activated. In this case, the RS can transmit the BCH informationreceived from the BS in the subframe #0 to the MS through the 2nd DL,and can receive a signal from the MS through the 2nd UL. In the subframe#1, the RS can transmit the SCH information to the MS. The SCHinformation transmitted by the RS to the MS may be SCH informationgenerated by the RS itself.

Unlike in FIG. 12, it is assumed that the BS does not have to transmitspecific control information to the RS in a subframe #5. Therefore, inthe subframe #5, the 2nd DL and the 2nd UL between the RS and the MS areactivated, and the 1st DL and the 1st UL between the BS and the RS areinactivated.

Next, in a subframe #6, the 2nd DL between the RS and the MS and the 1stUL between the BS and the RS are activated. In the subframe #6, the RStransmits control information to the MS. The control information may beSCH information generated by the RS. Therefore, the 2nd DL between theRS and the MS is activated, and the 1st DL between the BS and the RS isinactivated. In this case, the 1st UL between the BS and the RS or the2nd UL between the RS and the MS can be selectively activated. However,the 1st UL between the BS and the RS is preferably activated so thatsynchronous HARQ is performed for data transmission between the BS andthe RS.

As such, a link between the BS and the RS and a link between the RS andthe MS may be alternately activated according to a specific rule. Forexample, the link between the BS and the RS may be activated in anodd-numbered subframe, and the link between the RS and the MS may beactivated in an even-numbered subframe. The link between the BS and theRS may be activated in the even-numbered subframe, and the link betweenthe RS and the MS may be activated in the odd-numbered subframe.Alternatively, the link between the RS and the MS may be activated in asubframe indexed with a multiple of k. Alternatively, the link betweenthe RS and the MS may be activated in a subframe corresponding to apre-defined pattern. Accordingly, HARQ for data transmission between theRS and the MS can be performed using an activated subframe.

When the 1st DL is activated in a certain subframe, the 2nd DL isinactivated in that subframe. There may be a channel that must betransmitted from the RS to the MS through the 2nd DL in a specificsubframe, preferably, a specific control channel. The channel that mustbe transmitted to the MS may be at least one of an SCH, a BCH, and apaging channel. Preferably, the channel that must be transmitted to theMS may be at least one of a primary SCH, a secondary SCH, a physicalBCH, a dynamic BCH (D-BCH), and a paging channel. Therefore, by properlyconfiguring a subframe of the RS, the subframe can be configured so thatthe 1st DL is activated for some of the remaining subframes other thanthe specific subframe in which the channel that must be transmitted tothe MS through the 2nd DL exists. For example, if the specific subframeis subframes #0, #4, #5, and #9 of the RS, a subframe in which the 1stDL may be activated, that is, a subframe in which the 2nd DL may beinactivated, is subframes #1, #2, #3, #6, #7, and #8. In this case, thesubframe may be configured by considering an acknowledgement(ACK)/non-acknowledgement (NACK) transmission time, a dataretransmission time, etc., for data transmission. A delay from a DLtransmission time to a UL transmission time, a delay from the ULtransmission time to the DL transmission time, or the like may befurther considered.

FIG. 14 and FIG. 15 show link usage efficiency depending on the numberof HARQ processes when a subframe is configured according to anembodiment of the present invention.

An “HP” column indicates a subframe in which an HARQ process can besuccessfully performed. When taking an HP1 for example, in a subframe#0, data is initially transmitted from an RS to an MS through a 2nd DL.In a subframe #4, an ACK/NACK signal is transmitted from the MS to theRS through a 2nd UL. In a subframe #8, that is, after 8 subframes elapsefrom initial transmission, data is retransmitted (or initiallytransmitted) from the RS to the MS through the 2nd DL. A “Relay DL Tx”.column indicates whether the 2nd DL from the RS to the MS is used. A“Relay UL Rx” column indicates whether the 2nd UL from the MS to the RSis used. In the “Relay DL Tx” column and the “Relay UL Rx” column,indicates use, and “0” indicates non-use. A “Link Utilization (DL orUL)” column indicates a usage rate of the 2nd DL or the 2nd UL, and isexpressed by “1” when at least one of the 2nd DL and the 2nd UL is used,and is expressed by “0” when none of them is used. A “Link Utilization(DL and UL)” column indicates a usage rate of the 2nd DL and/or the 2ndUL, and is expressed by “2” when both of the 2nd DL and the 2nd UL areused, is expressed by “1” when any one of the 2nd DL and the 2nd UL isused, and is expressed by “0” when none of them is used. A “(n)” columnand a “(n+4)” column indicate a response transmitted from the MS to theRS through the 2nd UL in a subframe #n+4 with respect to a controlchannel transmitted from the RS to the MS through the 2nd DL in asubframe #n. It is assumed herein that a time required for the responseis 4 subframes.

Table 5 shows a result obtained by analyzing link usage efficiency basedon the example of FIG. 14. Table 6 shows a result obtained by analyzinglink usage efficiency based on the example of FIG. 15.

TABLE 5 RS to MS 1st Downlink Occupancy (No.) 28 1st Downlink Occupancy(%) 70 2nd Downlink availability (%) 30 MS to RS 1st Uplink Occupancy(No.) 28 1st Uplink Occupancy (%) 70 2nd Uplink availability (%) 30 DLor UL 1st Downlink and/or 1st Uplink Occupancy (No.) 40 1st Downlinkand/or 1st Uplink Occupancy (%) 100 2nd Downlink and 2nd UplinkOccupancy (%) 0 DL and UL 1st Downlink and 1st Uplink Occupancy (No.) 161st Downlink or 1st Uplink Occupancy (No.) 24 1st Downlink or 1st UplinkOccupancy (%) 70 2nd Downlink and/or 2nd Uplink Occupancy (%) 30

TABLE 6 RS to MS 1st Downlink Occupancy (No.) 28 1st Downlink Occupancy(%) 70 2nd Downlink availability (%) 30 MS to RS 1st Uplink Occupancy(No.) 28 1st Uplink Occupancy (%) 70 2nd Uplink availability (%) 30 DLor UL 1st Downlink and/or 1st Uplink Occupancy (No.) 32 1st Downlinkand/or 1st Uplink Occupancy (%) 80 2nd Downlink and 2nd Uplink Occupancy(%) 20 DL and UL 1st Downlink and 1st Uplink Occupancy (No.) 24 1stDownlink or 1st Uplink Occupancy (No.) 8 1st Downlink or 1st UplinkOccupancy (%) 70 2nd Downlink and/or 2nd Uplink Occupancy (%) 30

Referring to FIG. 14 and Table 5, when data is transmitted in eachsubframe from the RS to the MS through the 2nd DL in subframes #0 to #3,ACK/NACK is transmitted in each subframe from the MS to the RS throughthe 2nd UL in subframes #4 to #7. Data is transmitted in each subframefrom the RS to the MS through the 2nd DL in subframes #8 to #11, or thedata transmitted in the subframes #0 to #3 is retransmitted.Accordingly, there is no subframe in which the RS operates in a firstmode where the 1st UL and the 1st DL between the BS and the RS aresimultaneously activated.

Referring to FIG. 15 and Table 6, when data is transmitted from the RSto the MS through the 2nd DL in subframes #0, #2, #4, and #6, ACK/NACKis transmitted from the MS to the RS through the 2nd UL in subframes #4,#6, #8, and #10. Data is transmitted from the RS to the MS through the2nd DL in subframes #8, #10, #12, and #14, or the data transmitted inthe subframes #0, #2, #4, and #6 is retransmitted. 20% of all subframesare used for neither the 2nd DL nor the 2nd UL. Therefore, as for the20% of all subframes, the RS can operate in the first mode where the 1stDL and the 1st UL are simultaneously activated.

Link usage efficiency can be increased by configuring a subframe asshown in FIG. 15. That is, if the “Link Utilization (DL and UL)” columnis “0” or “2”, the RS can operate in the first mode where the 1st DL andthe 1st UL are simultaneously activated or the 2nd DL and the 2nd UL aresimultaneously activated. If the “Link Utilization (DL and UL)” columnis “1”, the RS can operate in a second mode where the 1st DL and the 2ndUL are simultaneously activated or the 2nd DL and the 1st UL aresimultaneously activated. For example, while operating in the firstmode, the RS may perform mode switching to the second mode according toa specific situation. Examples of the specific situation requiring modeswitching include a case where there is a control signal that must betransmitted in a specific subframe, a case where mode switching isnecessary to perform HARQ without difficulty, etc. In this case, anoperation mode of the RS may be switched by the RS itself or may beswitched by separate signaling with the BS or the MS. When the RSperforms separate signaling with the BS or the MS, the signaling processmay indicate a specific subframe in which the operation mode of the RSis switched or may indicate a rule of switching the operation mode.Alternatively, signaling may be performed with a specific period.

Collision can be reduced between a backhaul link and an access link byconfiguring a subframe as shown in FIG. 15. That is, in FIG. 15, among 8subframes, even-numbered subframes are allocated for the access link,and thus odd-numbered subframes can be allocated for the backhaul link.Alternatively, the even-numbered subframes may be allocated for thebackhaul link, and the odd-numbered subframes may be allocated for theaccess link. Unlike this, when subframes are allocated for the backhaullink and the access link in a different ratio, collision may occurbetween the backhaul link and the access link. For example, when 5subframes out of the 8 subframes are allocated for the backhaul, thebackhaul link uses all of 4 even-numbered (or odd-numbered) subframesout of the 8 subframes, and additionally uses the odd-numbered (oreven-numbered) subframes. In this case, the backhaul link may collidewith the access link. Therefore, subframes may be alternately allocatedin a ratio of 5:5 for the backhaul and the access link, thereby avoidingcollision between the backhaul and the access link. In this case, aconfiguration of subframes allocated for the backhaul and the accesslink may be received from the BS by signaling. For example, the BS andthe RS may share a configuration such as a ratio of subframes allocatedfor the backhaul and the access link (e.g., backhaul link:accesslink=5:5, 6:4, or 7:3), an allocation pattern of the subframes, etc.,and the BS may report an index for the configuration to the RS byperforming signaling.

FIG. 16 is a block diagram showing an RS according to an embodiment ofthe present invention.

Referring to FIG. 16, an RS 100 includes a radio frequency (RF) unit 110transmitting and receiving a radio signal, a processor 120, and a modeswitching unit 130. The processor 120 is configured to operate in afirst mode or a second mode. The first mode includes a first sub-modefor simultaneously activating a 1st DL and a 1st UL between a BS and theRS and a second sub-mode for simultaneously activating a 2nd DL and a2nd UL between the RS and an MS. The second mode includes a thirdsub-mode for simultaneously activating the 1st DL between the BS and theRS and the 2nd UL between the RS and the MS and a fourth sub-mode forsimultaneously activating the 1st UL between the BS and the RS and the2nd DL between the RS and the MS. The mode switching unit 130 isconfigured so that mode switching is performed between the first modeand the second mode by considering a specific subframe.

The aforementioned functions can be executed by processors such asmicroprocessors, controllers, microcontrollers, application specificintegrated circuits (ASICs) and so on according to software or programcodes coded to execute the functions. The design, development andimplementation of the codes are obvious to those skilled in the art.

While the present invention has been particularly shown an describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

What is claimed is:
 1. A method of operating a base station (BS) in awireless communication system, the method comprising: transmittingsubframe configuration information to a relay station (RS); andtransmitting a signal to the RS in a downlink subframe configured basedon the subframe configuration information, wherein a first downlinktransmission, from the BS to the RS, and a second downlink transmission,from the RS to a user equipment (UE), are performed at different timesand in a downlink frequency band, and wherein when a frame comprises 10downlink subframes, the downlink subframe for transmitting the signal tothe RS is configured per a specific number of subframes with anexception of a first downlink subframe, a fifth downlink subframe, asixth downlink subframe and a tenth downlink subframe of the frame. 2.The method of claim 1, wherein a first uplink transmission, from the RSto the BS, and a second uplink transmission, from the UE to the RS, areperformed at different times and in an uplink frequency band.
 3. Themethod of claim 2, wherein the frame comprises 10 downlink subframes inthe downlink frequency band and 10 uplink subframes in the uplinkfrequency band.
 4. The method of claim 1, wherein subframe configurationinformation is transmitted through a higher layer signal.
 5. A basestation (BS) comprising: a radio frequency (RF) unit that transmits andreceives a radio signal; and a processor, coupled to the RF unit, that:controls the RF unit to transmit subframe configuration information to arelay station (RS) and controls the RF unit to transmit a signal to theRS in a downlink subframe configured based on the subframe configurationinformation, wherein a first downlink transmission, from the BS to theRS, and a second downlink transmission, from the RS to a user equipment(UE), are performed at different times and in a downlink frequency band,and wherein when a frame comprises 10 downlink subframes, the downlinksubframe for transmitting the signal to the RS is configured per aspecific number of subframes with an exception of a first downlinksubframe, a fifth downlink subframe, a sixth downlink subframe and atenth downlink subframe of the frame.
 6. The BS of claim 5, wherein afirst uplink transmission, from the RS to the BS, and a second uplinktransmission, from the UE to the RS, are performed at different timesand in an uplink frequency band.
 7. The BS of claim 6, wherein the framecomprises 10 downlink subframes in the downlink frequency band and 10uplink subframes in the uplink frequency band.
 8. The BS of claim 5,wherein subframe configuration information is transmitted through ahigher layer signal.